I encrypted my SSD using BitLocker, and for me, the performance hit is not really noticable in my day-to-day work (programming + running a virtual machine). Your SSD will still be A LOT faster than a regular, unencrypted HDD. But YMMV.

This case is only relevant to SSDs with a sandforce controller, however -- as (only) the sandforce controller compresses data for increased speed, which cannot be done with encrypted data.